1. Technical Field of the Invention
The present invention relates to a separator for a solid electrolyte condenser wherein a solid electrolyte lies between an anode foil and a cathode foil, and relates to a rolled type solid electrolyte condenser using the separator.
2. Description of the Prior Art
As electronic devices are operated at higher frequency, the electrolyte condenser also is being desired to have a superior impedance characteristics at the higher frequency and a large capacitance. Recently, the rolled type solid electrolyte condenser using the solid electrolyte of high conductivity polymer has been studied in order to reduce the impedance at the higher frequency. On the other hand, the rolled type condenser wherein the anode foil and the cathode foil is rolled with the separator between has an advantage in increasing the capacitance, compared with laminated type condenser wherein the electrode foils are laminated, because the structure of the rolled type is suitable to increase the capacity. Therefore, the rolled type solid electrolyte condensers using the conductive polymer have been already manufactured.
In the rolled type solid electrolyte condenser, the separator for avoiding a contact of the anode foil with the cathode foil is indispensable. For example, one of the separator is the so-called carbonized paper which is a conventional electrolyte paper such as Manila hemp or kraft paper which is rolled in order to form the condenser and then is heated or other treatment for carbonization. Further, a nonwoven fabric of which main component is glass fiber or a resin manufactured by the dry melt blow method.
Further, in JP 10-340829 A (1998), the separator of the solid electrolyte condenser is made of a nonwoven fabric of which main component is a synthetic fiber which is a vinylon (a resin on the basis of polyvinylalchol, or a mixed nonwoven fabric of vinylon and other resin or resins.
The rolled type solid electrolyte condenser using the above-mentioned carbonized paper is manufactured by heating the condenser at a temperature higher than 250° C. However, a insulating oxide coat is damaged by the heating, thereby increasing a leak current. Further, the condenser is short-circuited at a higher rate, even when the condenser is repaired by aging. Further, the condenser of this type has a disadvantage that a highly oxidization resistive and costly silver plated lead wire must be used, because the plated layer such as tin/zinc layer of the conventional lead wire of the solid electrolyte condenser is oxidized by the heating, thereby reducing the wetting to a solder at a lead wire portion of the conventionally plated wire of a finished product.
The glass fiber nonwoven fabric electrolyte paper causes bad influences to working environments, due to scattering of the needle-like glass fibers during cutting and rolling them. Further, a bending strength of the paper during rolling is not sufficient enough to prevent the short-circuit in the finished products. Further, the glass fiber paper is thin and is difficult to be manufactured at a thickness of 40 to 50 μm. Even if a paper is manufactured at that thickness, the strength of the paper is so small that the paper can hardly be rolled. Thus, the glass fiber paper is not suitable for manufacturing recent small-sized electronic parts.
Further, a tensile strength of the nonwoven fabric of resin by dry method such as the melt blow method, vinylon nonwoven fabric and mixed nonwoven fabric of vinylon and other resins is weak, compared with the electrolyte paper. Therefore, the separator of the above-mentioned nonwoven fabric is frequently broken during rolling process of manufacturing the condenser, thereby causing a high rate of short circuit during the aging. Furthermore, it is difficult to manufacture a low impedance solid electrolyte condenser at higher frequency, because the conductive polymer can not easily be held to the separator due to an influence of adhesives for adhering the resin fibers in order to lower the impedance. Further, vinylon has several disadvantages, due to its poor heat resistivity, that vinylon condenser can not be used at a higher temperature, vinylon is easily dissolved during high temperature reflow of soldering, a sealing portion is easily damaged due to inner pressure rise due to an outgas, and electrical characteristics of the solid electrolyte condenser are easily degraded.
On the other hand, polyethylenedioxythiophene and polypyrrole is known as conductive polymers for the solid electrolyte. They are manufactured by the chemical oxydization polymerization of ethylenedioxythiophene by using an optimum oxydizing agent. However, it is difficult to hold them to the carbonized paper, the glass fiber nonwoven fabric and the nonwoven fabric of polypropylene manufacture by the wet method. Therefore, the impedance is increased and the capacitance is decreased, due to a separation of the conductive polymer from the separator due to a thermal stress and other factors. Accordingly, the conventional solid electrolyte condenser has a disadvantage that a size per capacitance ratio of the condenser using the above-mentioned conductive polymers becomes greater than that of a condenser using an electrolytic solution.